Directory synchronization of a dispersed storage network

ABSTRACT

A method begins by independently executing a first write transaction in a dispersed storage network (DSN) to a particular write verification step of a multiple step write process, wherein the first write transaction has a first transaction identifier. The method continues by independently executing a second write transaction in the DSN to the particular write verification step, wherein the second write transaction has a second transaction identifier, and wherein subject matter of the first write transaction is related to subject matter of the second write transaction. The method continues by dependently finalizing the multiple step write process for each of the first and second write transactions utilizing the first and second transaction identifiers when each of the first and second write transactions have reached the particular write verification step.

CROSS REFERENCE TO RELATED PATENTS

The present U.S. Utility patent application claims priority pursuant to35 U.S.C. §120 as a continuation of U.S. Utility application Ser. No.12/903,205, entitled, “DIRECTORY SYNCHRONIZATION OF A DISPERSED STORAGENETWORK,” filed Oct. 13, 2010, which is incorporated herein by referencein its entirety and made part of the present U.S. Utility patentapplication for all purposes.

U.S. Utility patent application Ser. No. 12/903,205 claims prioritypursuant to 35 U.S.C. §119(e) to U.S. Provisional Application No.61/290,775, entitled, “DISTRIBUTED STORAGE DATA SYNCHRONIZATION,” filedDec. 29, 2009; and claims priority pursuant to 35 U.S.C. §120 as acontinuation-in-part of U.S. Utility application Ser. No. 12/080,042,entitled, “REBUILDING DATA ON A DISPERSED STORAGE NETWORK,” filed Mar.31, 2008.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT—NOTAPPLICABLE INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACTDISC—NOT APPLICABLE BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

This invention relates generally to computing systems and moreparticularly to data storage solutions within such computing systems.

2. Description of Related Art

Computers are known to communicate, process, and store data. Suchcomputers range from wireless smart phones to data centers that supportmillions of web searches, stock trades, or on-line purchases every day.In general, a computing system generates data and/or manipulates datafrom one form into another. For instance, an image sensor of thecomputing system generates raw picture data and, using an imagecompression program (e.g., JPEG, MPEG, etc.), the computing systemmanipulates the raw picture data into a standardized compressed image.

With continued advances in processing speed and communication speed,computers are capable of processing real time multimedia data forapplications ranging from simple voice communications to streaming highdefinition video. As such, general-purpose information appliances arereplacing purpose-built communications devices (e.g., a telephone). Forexample, smart phones can support telephony communications but they arealso capable of text messaging and accessing the internet to performfunctions including email, web browsing, remote applications access, andmedia communications (e.g., telephony voice, image transfer, musicfiles, video files, real time video streaming. etc.).

Each type of computer is constructed and operates in accordance with oneor more communication, processing, and storage standards. As a result ofstandardization and with advances in technology, more and moreinformation content is being converted into digital formats. Forexample, more digital cameras are now being sold than film cameras, thusproducing more digital pictures. As another example, web-basedprogramming is becoming an alternative to over the air televisionbroadcasts and/or cable broadcasts. As further examples, papers, books,video entertainment, home video, etc., are now being stored digitally,which increases the demand on the storage function of computers.

A typical computer storage system includes one or more memory devicesaligned with the needs of the various operational aspects of thecomputer's processing and communication functions. Generally, theimmediacy of access dictates what type of memory device is used. Forexample, random access memory (RAM) memory can be accessed in any randomorder with a constant response time, thus it is typically used for cachememory and main memory. By contrast, memory device technologies thatrequire physical movement such as magnetic disks, tapes, and opticaldiscs, have a variable response time as the physical movement can takelonger than the data transfer, thus they are typically used forsecondary memory (e.g., hard drive, backup memory, etc.).

A computer's storage system will be compliant with one or more computerstorage standards that include, but are not limited to, network filesystem (NFS), flash file system (FFS), disk file system (DFS), smallcomputer system interface (SCSI), internet small computer systeminterface (iSCSI), file transfer protocol (FTP), and web-baseddistributed authoring and versioning (WebDAV). These standards specifythe data storage format (e.g., files, data objects, data blocks,directories, etc.) and interfacing between the computer's processingfunction and its storage system, which is a primary function of thecomputer's memory controller.

Despite the standardization of the computer and its storage system,memory devices fail; especially commercial grade memory devices thatutilize technologies incorporating physical movement (e.g., a discdrive). For example, it is fairly common for a disc drive to routinelysuffer from bit level corruption and to completely fail after threeyears of use. One solution is to utilize a higher-grade disc drive,which adds significant cost to a computer.

Another solution is to utilize multiple levels of redundant disc drivesto replicate the data into two or more copies. One such redundant driveapproach is called redundant array of independent discs (RAID). In aRAID device, a RAID controller adds parity data to the original databefore storing it across the array. The parity data is calculated fromthe original data such that the failure of a disc will not result in theloss of the original data. For example, RAID 5 uses three discs toprotect data from the failure of a single disc. The parity data, andassociated redundancy overhead data, reduces the storage capacity ofthree independent discs by one third (e.g., n−1=capacity). RAID 6 canrecover from a loss of two discs and requires a minimum of four discswith a storage capacity of n−2.

While RAID addresses the memory device failure issue, it is not withoutits own failure issues that affect its effectiveness, efficiency andsecurity. For instance, as more discs are added to the array, theprobability of a disc failure increases, which increases the demand formaintenance. For example, when a disc fails, it needs to be manuallyreplaced before another disc fails and the data stored in the RAIDdevice is lost. To reduce the risk of data loss, data on a RAID deviceis typically copied on to one or more other RAID devices. While thisaddresses the loss of data issue, it raises a security issue sincemultiple copies of data are available, which increases the chances ofunauthorized access. Further, as the amount of data being stored grows,the overhead of RAID devices becomes a non-trivial efficiency issue.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of a computingsystem in accordance with the invention;

FIG. 2 is a schematic block diagram of an embodiment of a computing corein accordance with the invention;

FIG. 3 is a schematic block diagram of an embodiment of a distributedstorage processing unit in accordance with the invention;

FIG. 4 is a schematic block diagram of an embodiment of a grid module inaccordance with the invention;

FIG. 5 is a diagram of an example embodiment of error coded data slicecreation in accordance with the invention;

FIG. 6 is another schematic block diagram of another embodiment of acomputing system in accordance with the invention;

FIG. 7 is another schematic block diagram of another embodiment of acomputing system in accordance with the invention;

FIG. 8 is another schematic block diagram of another embodiment of acomputing system in accordance with the invention;

FIG. 9 is a flowchart illustrating an example of selecting a dispersedstorage (DS) processing unit in accordance with the invention;

FIG. 10A is another schematic block diagram of another embodiment of acomputing system in accordance with the invention;

FIG. 10B is another schematic block diagram of another embodiment of acomputing system in accordance with the invention;

FIG. 11 is a flowchart illustrating an example of determining adispersed storage (DS) unit storage set in accordance with theinvention;

FIG. 12A is a schematic block diagram of an embodiment of a dispersedstorage network (DSN) memory in accordance with the invention;

FIG. 12B is another schematic block diagram of another embodiment of adispersed storage network (DSN) memory in accordance with the invention;

FIG. 13 is another schematic block diagram of another embodiment of acomputing system in accordance with the invention;

FIG. 14 is a flowchart illustrating an example of storing data inaccordance with the invention;

FIG. 15 is a flowchart illustrating an example of retrieving data inaccordance with the invention;

FIG. 16 is another flowchart illustrating another example of storingdata in accordance with the invention; and

FIG. 17 is a flowchart illustrating an example of storing an encodeddata slice in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of a computing system 10 thatincludes one or more of a first type of user devices 12, one or more ofa second type of user devices 14, at least one distributed storage (DS)processing unit 16, at least one DS managing unit 18, at least onestorage integrity processing unit 20, and a distributed storage network(DSN) memory 22 coupled via a network 24. The network 24 may include oneor more wireless and/or wire lined communication systems; one or moreprivate intranet systems and/or public internet systems; and/or one ormore local area networks (LAN) and/or wide area networks (WAN).

The DSN memory 22 includes a plurality of distributed storage (DS) units36 for storing data of the system. Each of the DS units 36 includes aprocessing module and memory and may be located at a geographicallydifferent site than the other DS units (e.g., one in Chicago, one inMilwaukee, etc.). The processing module may be a single processingdevice or a plurality of processing devices. Such a processing devicemay be a microprocessor, micro-controller, digital signal processor,microcomputer, central processing unit, field programmable gate array,programmable logic device, state machine, logic circuitry, analogcircuitry, digital circuitry, and/or any device that manipulates signals(analog and/or digital) based on hard coding of the circuitry and/oroperational instructions. The processing module may have an associatedmemory and/or memory element, which may be a single memory device, aplurality of memory devices, and/or embedded circuitry of the processingmodule. Such a memory device may be a read-only memory, random accessmemory, volatile memory, non-volatile memory, static memory, dynamicmemory, flash memory, cache memory, and/or any device that storesdigital information. Note that if the processing module includes morethan one processing device, the processing devices may be centrallylocated (e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that when the processing module implements one or more ofits functions via a state machine, analog circuitry, digital circuitry,and/or logic circuitry, the memory and/or memory element storing thecorresponding operational instructions may be embedded within, orexternal to, the circuitry comprising the state machine, analogcircuitry, digital circuitry, and/or logic circuitry. Still further notethat, the memory element stores, and the processing module executes,hard coded and/or operational instructions corresponding to at leastsome of the steps and/or functions illustrated in FIGS. 1-17.

Each of the user devices 12-14, the DS processing unit 16, the DSmanaging unit 18, and the storage integrity processing unit 20 may be aportable computing device (e.g., a social networking device, a gamingdevice, a cell phone, a smart phone, a personal digital assistant, adigital music player, a digital video player, a laptop computer, ahandheld computer, a video game controller, and/or any other portabledevice that includes a computing core) and/or a fixed computing device(e.g., a personal computer, a computer server, a cable set-top box, asatellite receiver, a television set, a printer, a fax machine, homeentertainment equipment, a video game console, and/or any type of homeor office computing equipment). Such a portable or fixed computingdevice includes a computing core 26 and one or more interfaces 30, 32,and/or 33. An embodiment of the computing core 26 will be described withreference to FIG. 2.

With respect to the interfaces, each of the interfaces 30, 32, and 33includes software and/or hardware to support one or more communicationlinks via the network 24 and/or directly. For example, interfaces 30support a communication link (wired, wireless, direct, via a LAN, viathe network 24, etc.) between the first type of user device 14 and theDS processing unit 16. As another example, DSN interface 32 supports aplurality of communication links via the network 24 between the DSNmemory 22 and the DS processing unit 16, the first type of user device12, and/or the storage integrity processing unit 20. As yet anotherexample, interface 33 supports a communication link between the DSmanaging unit 18 and any one of the other devices and/or units 12, 14,16, 20, and/or 22 via the network 24.

In general and with respect to data storage, the system 10 supportsthree primary functions: distributed network data storage management,distributed data storage and retrieval, and data storage integrityverification. In accordance with these three primary functions, data canbe distributedly stored in a plurality of physically different locationsand subsequently retrieved in a reliable and secure manner regardless offailures of individual storage devices, failures of network equipment,the duration of storage, the amount of data being stored, attempts athacking the data, etc.

The DS managing unit 18 performs distributed network data storagemanagement functions, which include establishing distributed datastorage parameters, performing network operations, performing networkadministration, and/or performing network maintenance. The DS managingunit 18 establishes the distributed data storage parameters (e.g.,allocation of virtual DSN memory space, distributed storage parameters,security parameters, billing information, user profile information,etc.) for one or more of the user devices 12-14 (e.g., established forindividual devices, established for a user group of devices, establishedfor public access by the user devices, etc.). For example, the DSmanaging unit 18 coordinates the creation of a vault (e.g., a virtualmemory block) within the DSN memory 22 for a user device (for a group ofdevices, or for public access). The DS managing unit 18 also determinesthe distributed data storage parameters for the vault. In particular,the DS managing unit 18 determines a number of slices (e.g., the numberthat a data segment of a data file and/or data block is partitioned intofor distributed storage) and a read threshold value (e.g., the minimumnumber of slices required to reconstruct the data segment).

As another example, the DS managing module 18 creates and stores,locally or within the DSN memory 22, user profile information. The userprofile information includes one or more of authentication information,permissions, and/or the security parameters. The security parameters mayinclude one or more of encryption/decryption scheme, one or moreencryption keys, key generation scheme, and data encoding/decodingscheme.

As yet another example, the DS managing unit 18 creates billinginformation for a particular user, user group, vault access, publicvault access, etc. For instance, the DS managing unit 18 tracks thenumber of times user accesses a private vault and/or public vaults,which can be used to generate a per-access bill. In another instance,the DS managing unit 18 tracks the amount of data stored and/orretrieved by a user device and/or a user group, which can be used togenerate a per-data-amount bill.

The DS managing unit 18 also performs network operations, networkadministration, and/or network maintenance. As at least part ofperforming the network operations and/or administration, the DS managingunit 18 monitors performance of the devices and/or units of the system10 for potential failures, determines the devices' and/or units'activation status, determines the devices' and/or units' loading, andany other system level operation that affects the performance level ofthe system 10. For example, the DS managing unit 18 receives andaggregates network management alarms, alerts, errors, statusinformation, performance information, and messages from the devices12-14 and/or the units 16, 20, 22. For example, the DS managing unit 18receives a simple network management protocol (SNMP) message regardingthe status of the DS processing unit 16.

The DS managing unit 18 performs the network maintenance by identifyingequipment within the system 10 that needs replacing, upgrading,repairing, and/or expanding. For example, the DS managing unit 18determines that the DSN memory 22 needs more DS units 36 or that one ormore of the DS units 36 needs updating.

The second primary function (i.e., distributed data storage andretrieval) begins and ends with a user device 12-14. For instance, if asecond type of user device 14 has a data file 38 and/or data block 40 tostore in the DSN memory 22, it sends the data file 38 and/or data block40 to the DS processing unit 16 via its interface 30. As will bedescribed in greater detail with reference to FIG. 2, the interface 30functions to mimic a conventional operating system (OS) file systeminterface (e.g., network file system (NFS), flash file system (FFS),disk file system (DFS), file transfer protocol (FTP), web-baseddistributed authoring and versioning (WebDAV), etc.) and/or a blockmemory interface (e.g., small computer system interface (SCSI), internetsmall computer system interface (iSCSI), etc.). In addition, theinterface 30 may attach a user identification code (ID) to the data file38 and/or data block 40.

The DS processing unit 16 receives the data file 38 and/or data block 40via its interface 30 and performs a distributed storage (DS) process 34thereon (e.g., an error coding dispersal storage function). The DSprocessing 34 begins by partitioning the data file 38 and/or data block40 into one or more data segments, which is represented as Y datasegments. For example, the DS processing 34 may partition the data file38 and/or data block 40 into a fixed byte size segment (e.g., 2¹ to2^(n) bytes, where n=>2) or a variable byte size (e.g., change byte sizefrom segment to segment, or from groups of segments to groups ofsegments, etc.).

For each of the Y data segments, the DS processing 34 error encodes(e.g., forward error correction (FEC), information dispersal algorithm,or error correction coding) and slices (or slices then error encodes)the data segment into a plurality of error coded (EC) data slices 42-48,which is represented as X slices per data segment. The number of slices(X) per segment, which corresponds to a number of pillars n, is set inaccordance with the distributed data storage parameters and the errorcoding scheme. For example, if a Reed-Solomon (or other FEC scheme) isused in an n/k system, then a data segment is divided into n slices,where k number of slices is needed to reconstruct the original data(i.e., k is the threshold). As a few specific examples, the n/k factormay be 5/3; 6/4; 8/6; 8/5; 16/10.

For each EC slice 42-48, the DS processing unit 16 creates a uniqueslice name and appends it to the corresponding EC slice 42-48. The slicename includes universal DSN memory addressing routing information (e.g.,virtual memory addresses in the DSN memory 22) and user-specificinformation (e.g., user ID, file name, data block identifier, etc.).

The DS processing unit 16 transmits the plurality of EC slices 42-48 toa plurality of DS units 36 of the DSN memory 22 via the DSN interface 32and the network 24. The DSN interface 32 formats each of the slices fortransmission via the network 24. For example, the DSN interface 32 mayutilize an internet protocol (e.g., TCP/IP, etc.) to packetize the ECslices 42-48 for transmission via the network 24.

The number of DS units 36 receiving the EC slices 42-48 is dependent onthe distributed data storage parameters established by the DS managingunit 18. For example, the DS managing unit 18 may indicate that eachslice is to be stored in a different DS unit 36. As another example, theDS managing unit 18 may indicate that like slice numbers of differentdata segments are to be stored in the same DS unit 36. For example, thefirst slice of each of the data segments is to be stored in a first DSunit 36, the second slice of each of the data segments is to be storedin a second DS unit 36, etc. In this manner, the data is encoded anddistributedly stored at physically diverse locations to improve datastorage integrity and security. Further examples of encoding the datasegments will be provided with reference to one or more of FIGS. 2-17.

Each DS unit 36 that receives an EC slice 42-48 for storage translatesthe virtual DSN memory address of the slice into a local physicaladdress for storage. Accordingly, each DS unit 36 maintains a virtual tophysical memory mapping to assist in the storage and retrieval of data.

The first type of user device 12 performs a similar function to storedata in the DSN memory 22 with the exception that it includes the DSprocessing. As such, the device 12 encodes and slices the data fileand/or data block it has to store. The device then transmits the slices11 to the DSN memory via its DSN interface 32 and the network 24.

For a second type of user device 14 to retrieve a data file or datablock from memory, it issues a read command via its interface 30 to theDS processing unit 16. The DS processing unit 16 performs the DSprocessing 34 to identify the DS units 36 storing the slices of the datafile and/or data block based on the read command. The DS processing unit16 may also communicate with the DS managing unit 18 to verify that theuser device 14 is authorized to access the requested data.

Assuming that the user device is authorized to access the requesteddata, the DS processing unit 16 issues slice read commands to at least athreshold number of the DS units 36 storing the requested data (e.g., toat least 10 DS units for a 16/10 error coding scheme). Each of the DSunits 36 receiving the slice read command, verifies the command,accesses its virtual to physical memory mapping, retrieves the requestedslice, or slices, and transmits it to the DS processing unit 16.

Once the DS processing unit 16 has received a read threshold number ofslices for a data segment, it performs an error decoding function andde-slicing to reconstruct the data segment. When Y number of datasegments has been reconstructed, the DS processing unit 16 provides thedata file 38 and/or data block 40 to the user device 14. Note that thefirst type of user device 12 performs a similar process to retrieve adata file and/or data block.

The storage integrity processing unit 20 performs the third primaryfunction of data storage integrity verification. In general, the storageintegrity processing unit 20 periodically retrieves slices 45, and/orslice names, of a data file or data block of a user device to verifythat one or more slices have not been corrupted or lost (e.g., the DSunit failed). The retrieval process mimics the read process previouslydescribed.

If the storage integrity processing unit 20 determines that one or moreslices is corrupted or lost, it rebuilds the corrupted or lost slice(s)in accordance with the error coding scheme. The storage integrityprocessing unit 20 stores the rebuild slice, or slices, in theappropriate DS unit(s) 36 in a manner that mimics the write processpreviously described.

FIG. 2 is a schematic block diagram of an embodiment of a computing core26 that includes a processing module 50, a memory controller 52, mainmemory 54, a video graphics processing unit 55, an input/output (IO)controller 56, a peripheral component interconnect (PCI) interface 58,an IO interface 60, at least one IO device interface module 62, a readonly memory (ROM) basic input output system (BIOS) 64, and one or morememory interface modules. The memory interface module(s) includes one ormore of a universal serial bus (USB) interface module 66, a host busadapter (HBA) interface module 68, a network interface module 70, aflash interface module 72, a hard drive interface module 74, and a DSNinterface module 76. Note the DSN interface module 76 and/or the networkinterface module 70 may function as the interface 30 of the user device14 of FIG. 1. Further note that the IO device interface module 62 and/orthe memory interface modules may be collectively or individuallyreferred to as IO ports.

The processing module 50 may be a single processing device or aplurality of processing devices. Such a processing device may be amicroprocessor, micro-controller, digital signal processor,microcomputer, central processing unit, field programmable gate array,programmable logic device, state machine, logic circuitry, analogcircuitry, digital circuitry, and/or any device that manipulates signals(analog and/or digital) based on hard coding of the circuitry and/oroperational instructions. The processing module 50 may have anassociated memory and/or memory element, which may be a single memorydevice, a plurality of memory devices, and/or embedded circuitry of theprocessing module 50. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, cache memory, and/or any devicethat stores digital information. Note that if the processing module 50includes more than one processing device, the processing devices may becentrally located (e.g., directly coupled together via a wired and/orwireless bus structure) or may be distributedly located (e.g., cloudcomputing via indirect coupling via a local area network and/or a widearea network). Further note that when the processing module 50implements one or more of its functions via a state machine, analogcircuitry, digital circuitry, and/or logic circuitry, the memory and/ormemory element storing the corresponding operational instructions may beembedded within, or external to, the circuitry comprising the statemachine, analog circuitry, digital circuitry, and/or logic circuitry.Still further note that, the memory element stores, and the processingmodule 50 executes, hard coded and/or operational instructionscorresponding to at least some of the steps and/or functions illustratedin FIGS. 1-17.

FIG. 3 is a schematic block diagram of an embodiment of a dispersedstorage (DS) processing module 34 of user device 12 and/or of the DSprocessing unit 16. The DS processing module 34 includes a gatewaymodule 78, an access module 80, a grid module 82, and a storage module84. The DS processing module 34 may also include an interface 30 and theDSnet interface 32 or the interfaces 68 and/or 70 may be part of userdevice 12 or of the DS processing unit 16. The DS processing module 34may further include a bypass/feedback path between the storage module 84to the gateway module 78. Note that the modules 78-84 of the DSprocessing module 34 may be in a single unit or distributed acrossmultiple units.

In an example of storing data, the gateway module 78 receives anincoming data object that includes a user ID field 86, an object namefield 88, and the data object field 40 and may also receivecorresponding information that includes a process identifier (e.g., aninternal process/application ID), metadata, a file system directory, ablock number, a transaction message, a user device identity (ID), a dataobject identifier, a source name, and/or user information. The gatewaymodule 78 authenticates the user associated with the data object byverifying the user ID 86 with the managing unit 18 and/or anotherauthenticating unit.

When the user is authenticated, the gateway module 78 obtains userinformation from the management unit 18, the user device, and/or theother authenticating unit. The user information includes a vaultidentifier, operational parameters, and user attributes (e.g., userdata, billing information, etc.). A vault identifier identifies a vault,which is a virtual memory space that maps to a set of DS storage units36. For example, vault 1 (i.e., user 1's DSN memory space) includeseight DS storage units (X=8 wide) and vault 2 (i.e., user 2's DSN memoryspace) includes sixteen DS storage units (X=16 wide). The operationalparameters may include an error coding algorithm, the width n (number ofpillars X or slices per segment for this vault), a read threshold T, awrite threshold, an encryption algorithm, a slicing parameter, acompression algorithm, an integrity check method, caching settings,parallelism settings, and/or other parameters that may be used to accessthe DSN memory layer.

The gateway module 78 uses the user information to assign a source name35 to the data. For instance, the gateway module 78 determines thesource name 35 of the data object 40 based on the vault identifier andthe data object. For example, the source name may contain a fileidentifier (ID), a vault generation number, a reserved field, and avault identifier (ID). As another example, the gateway module 78 maygenerate the file ID based on a hash function of the data object 40.Note that the gateway module 78 may also perform message conversion,protocol conversion, electrical conversion, optical conversion, accesscontrol, user identification, user information retrieval, trafficmonitoring, statistics generation, configuration, management, and/orsource name determination.

The access module 80 receives the data object 40 and creates a series ofdata segments 1 through Y 90-92 in accordance with a data storageprotocol (e.g., file storage system, a block storage system, and/or anaggregated block storage system). The number of segments Y may be chosenor randomly assigned based on a selected segment size and the size ofthe data object. For example, if the number of segments is chosen to bea fixed number, then the size of the segments varies as a function ofthe size of the data object. For instance, if the data object is animage file of 4,194,304 eight bit bytes (e.g., 33,554,432 bits) and thenumber of segments Y=131,072, then each segment is 256 bits or 32 bytes.As another example, if segment sized is fixed, then the number ofsegments Y varies based on the size of data object. For instance, if thedata object is an image file of 4,194,304 bytes and the fixed size ofeach segment is 4,096 bytes, the then number of segments Y=1,024. Notethat each segment is associated with the same source name.

The grid module 82 receives the data segments and may manipulate (e.g.,compression, encryption, cyclic redundancy check (CRC), etc.) each ofthe data segments before performing an error coding function of theerror coding dispersal storage function to produce a pre-manipulateddata segment. After manipulating a data segment, if applicable, the gridmodule 82 error encodes (e.g., Reed-Solomon, Convolution encoding,Trellis encoding, etc.) the data segment or manipulated data segmentinto X error coded data slices 42-44.

The value X, or the number of pillars (e.g., X=16), is chosen as aparameter of the error coding dispersal storage function. Otherparameters of the error coding dispersal function include a readthreshold T, a write threshold W, etc. The read threshold (e.g., T=10,when X=16) corresponds to the minimum number of error-free error codeddata slices required to reconstruct the data segment. In other words,the DS processing module 34 can compensate for X-T (e.g., 16−10=6)missing error coded data slices per data segment. The write threshold Wcorresponds to a minimum number of DS storage units that acknowledgeproper storage of their respective data slices before the DS processingmodule indicates proper storage of the encoded data segment. Note thatthe write threshold is greater than or equal to the read threshold for agiven number of pillars (X).

For each data slice of a data segment, the grid module 82 generates aunique slice name 37 and attaches it thereto. The slice name 37 includesa universal routing information field and a vault specific field and maybe 48 bytes (e.g., 24 bytes for each of the universal routinginformation field and the vault specific field). As illustrated, theuniversal routing information field includes a slice index, a vault ID,a vault generation, and a reserved field. The slice index is based onthe pillar number and the vault ID and, as such, is unique for eachpillar (e.g., slices of the same pillar for the same vault for anysegment will share the same slice index). The vault specific fieldincludes a data name, which includes a file ID and a segment number(e.g., a sequential numbering of data segments 1-Y of a simple dataobject or a data block number).

Prior to outputting the error coded data slices of a data segment, thegrid module may perform post-slice manipulation on the slices. Ifenabled, the manipulation includes slice level compression, encryption,CRC, addressing, tagging, and/or other manipulation to improve theeffectiveness of the computing system.

When the error coded data slices of a data segment are ready to beoutputted, the grid module 82 determines which of the DS storage units36 will store the EC data slices based on a dispersed storage memorymapping associated with the user's vault and/or DS storage unitattributes. The DS storage unit attributes may include availability,self-selection, performance history, link speed, link latency,ownership, available DSN memory, domain, cost, a prioritization scheme,a centralized selection message from another source, a lookup table,data ownership, and/or any other factor to optimize the operation of thecomputing system. Note that the number of DS storage units 36 is equalto or greater than the number of pillars (e.g., X) so that no more thanone error coded data slice of the same data segment is stored on thesame DS storage unit 36. Further note that EC data slices of the samepillar number but of different segments (e.g., EC data slice 1 of datasegment 1 and EC data slice 1 of data segment 2) may be stored on thesame or different DS storage units 36.

The storage module 84 performs an integrity check on the outboundencoded data slices and, when successful, identifies a plurality of DSstorage units based on information provided by the grid module 82. Thestorage module 84 then outputs the encoded data slices 1 through X ofeach segment 1 through Y to the DS storage units 36. Each of the DSstorage units 36 stores its EC data slice(s) and maintains a localvirtual DSN address to physical location table to convert the virtualDSN address of the EC data slice(s) into physical storage addresses.

In an example of a read operation, the user device 12 and/or 14 sends aread request to the DS processing unit 16, which authenticates therequest. When the request is authentic, the DS processing unit 16 sendsa read message to each of the DS storage units 36 storing slices of thedata object being read. The slices are received via the DSnet interface32 and processed by the storage module 84, which performs a parity checkand provides the slices to the grid module 82 when the parity check wassuccessful. The grid module 82 decodes the slices in accordance with theerror coding dispersal storage function to reconstruct the data segment.The access module 80 reconstructs the data object from the data segmentsand the gateway module 78 formats the data object for transmission tothe user device.

FIG. 4 is a schematic block diagram of an embodiment of a grid module 82that includes a control unit 73, a pre-slice manipulator 75, an encoder77, a slicer 79, a post-slice manipulator 81, a pre-slice de-manipulator83, a decoder 85, a de-slicer 87, and/or a post-slice de-manipulator 89.Note that the control unit 73 may be partially or completely external tothe grid module 82. For example, the control unit 73 may be part of thecomputing core at a remote location, part of a user device, part of theDS managing unit 18, or distributed amongst one or more DS storageunits.

In an example of write operation, the pre-slice manipulator 75 receivesa data segment 90-92 and a write instruction from an authorized userdevice. The pre-slice manipulator 75 determines if pre-manipulation ofthe data segment 90-92 is required and, if so, what type. The pre-slicemanipulator 75 may make the determination independently or based oninstructions from the control unit 73, where the determination is basedon a computing system-wide predetermination, a table lookup, vaultparameters associated with the user identification, the type of data,security requirements, available DSN memory, performance requirements,and/or other metadata.

Once a positive determination is made, the pre-slice manipulator 75manipulates the data segment 90-92 in accordance with the type ofmanipulation. For example, the type of manipulation may be compression(e.g., Lempel-Ziv-Welch, Huffman, Golomb, fractal, wavelet, etc.),signatures (e.g., Digital Signature Algorithm (DSA), Elliptic Curve DSA,Secure Hash Algorithm, etc.), watermarking, tagging, encryption (e.g.,Data Encryption Standard, Advanced Encryption Standard, etc.), addingmetadata (e.g., time/date stamping, user information, file type, etc.),cyclic redundancy check (e.g., CRC32), and/or other data manipulationsto produce the pre-manipulated data segment.

The encoder 77 encodes the pre-manipulated data segment 92 using aforward error correction (FEC) encoder (and/or other type of erasurecoding and/or error coding) to produce an encoded data segment 94. Theencoder 77 determines which forward error correction algorithm to usebased on a predetermination associated with the user's vault, a timebased algorithm, user direction, DS managing unit direction, controlunit direction, as a function of the data type, as a function of thedata segment 92 metadata, and/or any other factor to determine algorithmtype. The forward error correction algorithm may be Golay,Multidimensional parity, Reed-Solomon, Hamming, Bose Ray ChauduriHocquenghem (BCH), Cauchy-Reed-Solomon, or any other FEC encoder. Notethat the encoder 77 may use a different encoding algorithm for each datasegment 92, the same encoding algorithm for the data segments 92 of adata object, or a combination thereof.

The encoded data segment 94 is of greater size than the data segment 92by the overhead rate of the encoding algorithm by a factor of X/T, whereX is the width or number of slices, and T is the read threshold. In thisregard, the corresponding decoding process can accommodate at most X-Tmissing EC data slices and still recreate the data segment 92. Forexample, if X=16 and T=10, then the data segment 92 will be recoverableas long as 10 or more EC data slices per segment are not corrupted.

The slicer 79 transforms the encoded data segment 94 into EC data slicesin accordance with the slicing parameter from the vault for this userand/or data segment 92. For example, if the slicing parameter is X=16,then the slicer 79 slices each encoded data segment 94 into 16 encodedslices.

The post-slice manipulator 81 performs, if enabled, post-manipulation onthe encoded slices to produce the EC data slices. If enabled, thepost-slice manipulator 81 determines the type of post-manipulation,which may be based on a computing system-wide predetermination,parameters in the vault for this user, a table lookup, the useridentification, the type of data, security requirements, available DSNmemory, performance requirements, control unit directed, and/or othermetadata. Note that the type of post-slice manipulation may includeslice level compression, signatures, encryption, CRC, addressing,watermarking, tagging, adding metadata, and/or other manipulation toimprove the effectiveness of the computing system.

In an example of a read operation, the post-slice de-manipulator 89receives at least a read threshold number of EC data slices and performsthe inverse function of the post-slice manipulator 81 to produce aplurality of encoded slices. The de-slicer 87 de-slices the encodedslices to produce an encoded data segment 94. The decoder 85 performsthe inverse function of the encoder 77 to recapture the data segment90-92. The pre-slice de-manipulator 83 performs the inverse function ofthe pre-slice manipulator 75 to recapture the data segment 90-92.

FIG. 5 is a diagram of an example of slicing an encoded data segment 94by the slicer 79. In this example, the encoded data segment 94 includesthirty-two bits, but may include more or less bits. The slicer 79disperses the bits of the encoded data segment 94 across the EC dataslices in a pattern as shown. As such, each EC data slice does notinclude consecutive bits of the data segment 94 reducing the impact ofconsecutive bit failures on data recovery. For example, if EC data slice2 (which includes bits 1, 5, 9, 13, 17, 25, and 29) is unavailable(e.g., lost, inaccessible, or corrupted), the data segment can bereconstructed from the other EC data slices (e.g., 1, 3 and 4 for a readthreshold of 3 and a width of 4).

FIG. 6 is another schematic block diagram of another embodiment of acomputing system. As illustrated, the system includes a plurality ofuser devices 14, a network 24, a dispersed storage (DS) processing unit16, and a dispersed storage network (DSN) memory 22. Note that the DSNmemory 22 may be operably coupled to the DS processing unit 16 directlyor via the network 24. As illustrated, the DS processing unit 16includes a DS processing 34 and a plurality of functional layers toenable the DS processing 34 to interface with the plurality of userdevices 14. As illustrated, functional layers interface with otherfunctional layers above and below the functional layer converting oneset of protocols and/or procedures to the next as discussed in moredetail below.

As illustrated, there are at least two primary methods to interface theplurality of user devices 14 to the DS processing 34. A first primarymethod is an object method and a second primary method is a blockmethod. In the object method, data is interchanged in the form of anobject that may have variable size, name(s), directory links, andmetadata. Object storage includes a sequence of bytes of a varyinglength to help abstract the physical storage (e.g., object names ratherthan just disk drive locations). User devices can add/delete bytes of anobject. The object may have attached metadata describing the data. Thislayer looks like an object storage device to the above layers. Forexample, different size files and/or data associated with aclient/server application. In the block method, data is interchanged inthe form of fixed length blocks. Block storage utilizes a sequence ofbytes of a nominal length to help abstract the physical storage (e.g.,block numbers rather than just disk drive locations). Files may beconverted to blocks such that files typically fill multiple blocks. Theblock storage system can be abstracted by a file system for the userdevice.

Within the object method there are at least two secondary interfacingmethods. A first secondary method is a simple object method and a secondsecondary method is a file system method. In the simple object method,data is interchanged that may not conform to a typical computer file anddirectory system. Simple objects include data without a file structuresuch as bytes exchanged in an embedded client with a server application.Simple objects may be communicated in messages via HTTP. Simple objectsmay utilize simple object access protocol (SOAP) procedures to exchangeextensible markup language (XML) style documents. For example, locationdata exchanged between a global positioning system (GPS) equipped userdevice and a location services application server. In the file systemmethod, an approach is provided for storing and organizing data wherethe data is interchanged conforming to a typical computer file anddirectory system. In the file system, file names are assigned to filesand organized in a directory. File name may be an index into a fileallocation table (FAT) of location information. For example, a userdevice sends a Windows formatted file to the DSN system.

As illustrated, the DS processing unit 16 interfaces the DSN memory 22to the plurality of user devices 14 through either an object layer 142and/or a block layer 144. The object layer 142 interfaces with either asimple object layer 132 and/or a file system layer 138. As illustrated,the simple object layer 142 interfaces with either a Java SDK (softwaredeveloper kit) layer 114 and/or a web service layer 132. In an example,the Java SDK layer 114 may utilize a loader to interpret Java classfiles generated by a Java compiler. For instance, a Java archiver maymanage Java Archive (JAR) files. In an example, the web service layer132 utilizes a protocol for machine to machine interaction over anetwork. For instance, the protocol includes a simple object accessprotocol (SOAP) standard over hypertext protocol (HTTP) orrepresentational state transfer (REST). The web service layer 132interfaces with a HTTP/REST API layer 116. In example, the REST APIlayer on 16 utilizes a client server approach with discrete stateswithout a continuous server load (e.g., a request followed by a responsewith no state maintained by a server). Note that REST may run over HTTP.

As illustrated, the file system layer 138 interfaces with either a FTP(file transfer protocol) layer 118, an AFP (Apple Filing Protocol) layer120, and/or a Web DAV (web based distributed authoring and versioning)layer 122. In example, the FTP layer 118 is utilized to exchange filesover transport control protocol/internet protocol (TCP/IP) such as theinternet via ports. For instance, FTP utilizes a client server approach.For instance, FTP may utilize separate control and data streams andapplications may be command line or graphical. Note that a securesockets layer (SSL) and/or transport layer security (TLS) may be addedfor improved security. In an example, the AFP layer 120 provides anetwork protocol of file services for the Macintosh operating system(OS) family over TCP/IP. In an example, the Web DAV layer 122 providesextensions to HTTP to allow the plurality of user devices 14 to create,change, and/or move files on a web server. For instance, Windows OSprovides directory web folders.

As illustrated, the block layer of 44 interfaces with a SCSI (smallcomputer system interface) layer 140. In an example, the SCSI layer 140provides a bus approach physical connection and data transfer betweencomputers and peripheral devices. For instance, SCSI enables initiators(e.g., in user device) to send commands to targets (e.g., in DSprocessing unit and/or DS memory). The SCSI layer 140 interfaces with aniSCSI (internet small computer system interface) layer 134. In anexample, the iSCSI layer 134 transfers SCSI commands over the internetand/or the network 24 via TCP/IP enabling remote initiators (e.g., inuser device 14) to send commands to targets (e.g., in DS processing unit16 and/or DS unit 36).

As illustrated, the iSCSI layer 134 interfaces with a NFS (network filesystem) layer 124, a FTP layer 126, an AFP layer 128, a CIFS (commoninternet file system) layer 130, and/or directly with the user device14. In example, the NFS layer 124 enables user devices access over anetwork 24 where the DS processing unit 16 implements a NFS daemonprocess to make data available to a plurality of user devices 14. Forinstance, directories are communicated as user device 14 requests amount. In an example, the CIFS layer 130 provides a client serverapplication layer network protocol to provide shared access to files,printers, serial ports (e.g., common in Windows OS). The FTP layer 126and AFP layer 128 function as previously discussed.

In an example of operation, the user device 14 utilizes an embeddedinterface 102 to store data 108 in the DSN memory 22. A user device dataapplication communicates REST transfers via HTTP over the network to theHTTP/REST API interface layer 116. The web service layer 132 may hostthe server side of the REST transfers. The object layer 142 interfacesthe data to the DS processing 34 where the data is segmented, encoded,and sliced in accordance with an error coded dispersal storage functionto produce encoded data slices 11. The DS processing 34 sends theencoded data slices 11 to the DSN memory 22 for storage therein.

In another example of operation, the user device 14 utilizes a URLinterface (uniform resource locator) 104 to store a file 110 in the DSNmemory 22. A user device file application communicates Web DAV transfersvia HTTP over the network 24 to the Web DAV interface layer 122. The WebDAV interface 122 may provide web folders to the user device 14 suchthat the user device 14 may drop the file 110 to be stored in the DSNmemory 22 into the folder. The file system layer 138 and the objectlayer 142 interfaces data of the file 110 to the DS processing 34 wherethe data is segmented, encoded, and sliced in accordance with an errorcoded dispersal storage function to produce encoded data slices 11. TheDS processing 34 sends the encoded data slices 11 to the DSN memory 22for storage therein.

In another example of operation, the user device 14 utilizes a harddrive style interface to store data blocks 112 in the DSN memory 22. Auser device block application communicates CIFS transfers over thenetwork 24 to the CIFS interface layer 130. The CIFS interface layer 130may provide shared access to the user device 14 such that the userdevice when 14 looks at the DSN memory 22 as an iSCI device to storedata blocks 112 in the DSN memory 22. The iSCSI 134 and SCSI layer 140interfaces data of the data blocks 112 to the DS processing 34 where thedata is segmented, encoded, and sliced in accordance with an error codeddispersal storage function to produce encoded data slices 11. The DSprocessing 34 sends the encoded data slices 11 to the DSN memory 22 forstorage therein.

FIG. 7 is another schematic block diagram of another embodiment of acomputing system. As illustrated, the system includes a user device 12,a network 24, and a DSN memory 22. As illustrated, the user device 12includes a plurality of functional layers including a DS processing 34where the DS processing 34 interfaces with the DSN memory 22 and aplurality of interfacing functions 114-144 that interface with aplurality of applications 146-150. The interfacing functions 114-144operate as discussed with reference to FIG. 6.

There are at least two primary interfacing methods from the DSprocessing 34 to the applications 146-150. A first primary method is anobject method and a second primary method is a block method aspreviously discussed with reference to FIG. 6. As illustrated, a dataapplication 146 interfaces with the Java SDK layer 114 and/or HTTP/RESTAPI layer 116 interfacing functions. As illustrated, a file application148 interfaces with a FTP layer 118, an AFP layer 120, and/or a Web DAVlayer 122 interfacing functions. As illustrated, a block application 150interfaces with a NFS layer 124, a FTP layer 126, an AFP layer 128, aCIFS layer 130, and/or directly with an iSCSI layer 134. In anotherexample, the applications 146-150 may interface directly with one ormore of a web service layer 132, a simple object layer 136, a filesystem layer 138, the iSCSI layer 134, an object layer 142, and a blocklayer 144.

The applications 146-150 may utilize protocols (e.g., above the physicallayer) of the interfacing functions 114-144 to access the DSN memory 22.The data application 146 communicates data with the DS processing 34 toaccess the DSN memory 22. The file application 148 communicates fileswith the DS processing 34 to access the DSN memory 22. The blockapplication 150 communicates data blocks with the DS processing 34 toaccess the DSN memory 22. The DS processing sends slices 11 through thenetwork 24 to the DSN memory 22 for storage therein. The DS processing34 retrieves slices 11 from the DSN memory 22 through the network 24.

FIG. 8 is another schematic block diagram of another embodiment of acomputing system. As illustrated, the system includes a plurality ofuser devices 1-u, a plurality of DS processing units 1-p, and a DSNmemory 22. In an example of operation, the user device 1 may determine aDS processing unit 3 to utilize based on matching DS processing unitattributes to DS processing unit requirements. In another example, userdevice 2 determines to utilize DS processing unit 3 when DS processingunit 3 has the most favorable availability history of the plurality ofDS processing units 1-p and DS processing unit 3 is expected to continueto be available at a level that compares favorably with the user device2 DS processing unit requirements.

In another example of operation, the user device 6 may determine a DSprocessing unit 5 to utilize based on a predetermination and/orinitially on a predetermination followed by a potential subsequentmodification based in part on actual performance. In another example,user device 3 determines to initially utilize DS processing unit 1 whenDS processing unit 1 is listed in a predetermined table. Next, userdevice 3 determines to subsequently utilize DS processing unit 2 when DSprocessing unit 1 does not perform to a required level and DS processingunit 2 is the second choice.

In an example of operation, user device 7 provides DSN memory accessauthorization credentials when accessing the DSN memory 22 via DSprocessing unit 10. Next, the DS processing unit 10 verifies theauthorization credentials. The DS processing unit 10 forwards a DSNmemory access request to the DSN memory 22 when the authorizationcredential verification is favorable (e.g., on a list of authorizedusers for the particular item in the DSN memory 22). The DS processingunit 10 does not forward a DSN memory access request to the DSN memory22 when the authorization credential verification is not favorable(e.g., not on a list of authorized users for the particular item in theDSN memory 22). The method of operation of the user device 1-u todetermine the DS processing unit 1-p is discussed in greater detail withreference to FIG. 9.

In another sample, DS processing unit 3 forwards the authorizationcredentials to the DSN memory 22 with the DSN memory access request(e.g., without verification by the DS processing unit 3). The DSN memory22 verifies the authorization credentials. The DSN memory 22 processesthe memory access request when the authorization credential verificationis favorable. The DSN memory 22 does not process the memory accessrequest when the authorization credential verification is not favorable.

FIG. 9 is a flowchart illustrating an example of selecting a dispersedstorage (DS) processing unit. The method begins at step 152 where aprocessing module (e.g., of a user device) determines dispersed storagenetwork (DSN) memory access requirements. The requirements may includeone or more of security requirements, performance requirements, andpriority requirements. Such a determination may be based on one or moreof a query, a data type, a data size, a security indicator, aperformance indicator, a command, a predetermination, and a lookup.

The method continues at step 154 where the processing module determinescandidate DS processing units based on one or more of a virtual DSNaddress to physical location table, a query, a message from one or moreDS processing units, a data type, a data size, a security indicator, aperformance indicator, a status indicator, a command, apredetermination, and a lookup. The method continues at step 156 wherethe processing module determines candidate DS processing unitsattributes where the attributes may include one or more of currentcapacity, current loading, uptime history, performance history, datatypes supported, data types not supported, security restrictions, andencryption algorithms supported. Such a determination may be based onone or more of a virtual DSN address to physical location table, aquery, a message from one or more DS processing units, a data type, adata size, a security indicator, a performance indicator, a command, apredetermination, and a lookup. In an example, the processing moduledetermines that DS processing unit 1 has an attribute of capacity abovea threshold based on the performance indicator. In another example, theprocessing module determines that DS processing unit 4 has an attributeof a particular encryption algorithm based on the security indicatorfrom a query.

The method continues at step 158 where the processing module determinesa DS processing unit to utilize based on one or more of the DSN accessrequirements, the candidate DS processing units, the candidateprocessing units attributes, a comparison of the candidate processingunits attributes to the DSN access requirements, a virtual DSN addressto physical location table, a query, a message from one or more DSprocessing units, a data type, a data size, a security indicator, aperformance indicator, a command, a predetermination, and a lookup. Inan example, the processing module determines the DS processing unit suchthat substantially all of the requirements are met or exceeded. Forinstance, the processing module determines the DS processing unit thatmeets or exceeds the most requirements. The method continues at step 160where the processing module utilizes the determined DS processing unitfor the DSN access (e.g., store, retrieve, delete, check status).

FIG. 10A is another schematic block diagram of another embodiment of acomputing system and FIG. 10B is another schematic block diagram ofanother embodiment of a computing system. As illustrated in FIG. 10A,the system includes a user device 14, a dispersed storage (DS)processing unit 16, and a dispersed storage network (DSN) memory storageset 1. The system of FIG. 10B includes the user device 14, the DSprocessing unit 16, the DSN memory storage set 1, and a DSN memorystorage set 2 (e.g., to affect capacity expansion). As illustrated, theDSN memory storage sets 1 and 2 include a plurality of dispersed storage(DS) units 1-4 to accommodate a vault with a pillar width n=4. Forinstance, pillar 1 slices are stored in DS unit 1, pillar 2 slices arestored in DS unit 2, pillar 3 slices are stored in DS unit 3, and pillar4 slices are stored in DS unit 4. Note that the DSN memory storage sets1 and 2 may include any number of DS units.

In an example of operation, the DS processing unit 16 determines ifmemory utilization of DSN memory storage set 1 is above a threshold(e.g., when the memory utilization is greater than or equal to 70%utilized). Such a determination may be based on one or more of a queryof one or more of the DS units 1-4 of the DSN memory storage set 1, amessage from a DS managing unit, and/or a message from the DSN memorystorage set 1. Next, the DS processing unit 16 sends a memoryutilization alert to the DS managing unit when the DS processing unit 16determines that the memory utilization is above the threshold. Inaddition, the DS processing unit 16 may activate a dormant DSN memorystorage set as DSN memory storage set 2 to provide more storage capacityfor at least one vault that is utilizing DSN memory storage set 1.

In another example of operation, the DS processing unit 16 determineswhich of the two storage sets to utilize when the DS processing unit 16has new data to send to the DSN memory for storage. As illustrated inFIG. 10B, DSN memory storage set 2 has the same number of DS units asDSN memory storage set 1. In another example, DSN memory storage set 2may include two or more DS units for each pillar.

In another example of operation, the DS processing unit 16 determines tosend pillar 1 slices to DS unit 1 of DSN memory storage set 2. Inanother example, the DS processing unit 16 determines to send pillar 1slices to DS unit 1 of DSN memory storage set 1. Note that DSN memorystorage set 1 may be nearly full while DSN memory storage set 2 may benearly empty. In another example of operation, the DS processing unit 16balances distribution of new data between the two DSN memory storagesets to achieve a balancing objective. For instance, the balancingobjective may include completely filling DSN memory storage set 1followed by sending subsequent data to DSN memory storage set 2. Inanother instance, the balancing objective may include alternatingsending new data to the DSN memory storage sets such that DSN memorystorage set 1 fills up to capacity first. In yet another instance, thebalancing objective may include alternating sending new data to the DSNmemory storage sets such that the DSN memory storage sets fill up tocapacity substantially simultaneously. The DS processing method tobalance the utilization is discussed in greater detail with reference toFIG. 11.

FIG. 11 is a flowchart illustrating an example of determining adispersed storage (DS) unit storage set. The method begins at step 162where a processing module (e.g., of one of a dispersed storage (DS)processing unit, a user device, a dispersed storage (DS) managing unit,a storage integrity processing unit, or a dispersed storage (DS) unit)receives a store data object message (e.g., from one of the user device,the DS processing unit, the DS managing unit, the storage integrityprocessing unit, or the DS unit). Such a store data object message mayinclude one or more of a data object, a command, a user ID, a dataobject name, a data type, a data size, a priority indicator, a securityindicator, a performance indicator, and other metadata.

The method continues at step 164 where the processing module determinesoperational parameters based on one or more of the data object, a vaultlookup, a query of dispersed storage network (DSN) memory storage setmemory utilization, a command, a user ID, a data object name, a datatype, a data size, a priority indicator, a security indicator, aperformance indicator, and other metadata. For example, the processingmodule determines that the pillar width is four based on the user ID.The method continues at step 166 where the processing module determinesavailable DSN memory storage set(s) based on one or more of a query, theoperational parameters, a vault lookup, a predetermination, a query ofDSN memory storage set memory utilization, a command, a user ID, a dataobject name, a data type, a data size, a priority indicator, a securityindicator, a performance indicator, and other metadata. For example, theprocessing module determines that DSN memory storage sets 1 and 2 areavailable based on a query.

The method continues at step 168 where the processing module determinesa DSN memory storage set to utilize based on one or more of theavailable storage set(s), a balancing objective, a query, theoperational parameters, a vault lookup, a predetermination, a randomnumber, a query of DSN memory storage set memory utilization, a command,a user ID, a data object name, a data type, a data size, a priorityindicator, a security indicator, a performance indicator, and othermetadata. In an example, the processing module determines that thebalancing objective is to alternate sending new data to the availableDSN memory storage sets such that the DSN memory storage sets fill up tocapacity substantially simultaneously and that available DSN memorystorage set 1 has 30% capacity remaining and DSN memory storage set 2has 95% capacity remaining. For instance, the processing moduledetermines a random number from 1 to 125 (e.g., 30+95=125). Next, theprocessing module encodes the data object in accordance with an errorcoding dispersal storage function to produce encoded data slices. Theprocessing module sends the encoded data slices to DSN memory storageset 1 for storage therein when the random number is less than or equalto 30. The processing module sends the encoded data slices to DSN memorystorage set 2 for storage therein when the random number is greater than30. Note that this weighted method balances the utilization to meet thebalancing objective.

FIG. 12A is a schematic block diagram of an embodiment of a dispersedstorage network (DSN) memory and FIG. 12B is another schematic blockdiagram of another embodiment of a dispersed storage network (DSN)memory. As illustrated in FIG. 12A, the DSN memory includes a dispersedstorage (DS) unit 1 at site 1. As illustrated, DS unit 1 includes astorage unit control module 170 and a plurality of memories 1-12. Thestorage unit control module 170 may be implemented with the computingcore 26 of FIG. 2. The memories 1-12 may be implemented by one or moreof a magnetic hard disk, NAND flash, read only memory, optical disk,and/or any other type of read-only, or read/write memory. The memoriesmay be implemented as part of or outside of the DS unit 1. For example,memories 1-4 may be implemented in the DS unit 1 and memories 5-12 maybe implemented in a remote server (e.g., a different DS unit operablycoupled to the DS unit 1 via the network 24). In another example,memories 1-8 are implemented with the magnetic hard disk technology andmemories 9-12 are implemented with the NAND flash technology.

As illustrated in FIG. 12B, the DSN memory includes the DS unit 1 atsite 1 and a DS unit 2 at site 2 at a time subsequent to that of FIG.12A. As illustrated, DS unit 1 includes the storage and control module170 and memories 1-6. As illustrated, DS unit 2 includes the storageunit control module 170 and memories 7-12. Note that memories 1-12 aretransportable such that memories 7-12 were transferred to DS unit 2while memories 1-6 remain in DS unit 1.

As illustrated, the storage unit control module 170 is operably coupledto the computing system via the network 24. The storage unit controlmodule 24 may include DS processing 34 and may receive, via the network,a store command, metadata, and a data object to store. Note that the DSunit access may be via a WebDAV sequence, e.g., via an IP address suchas http://21.8.44/vault1 to facilitate easy DS unit access. The dataobject may include a simple object file, a block file, and/or EC dataslices. In an example, the storage unit control module 170 stores thedata object in one or more of the memories 1-12 substantially asreceived (e.g., a slice is stored as a slice, a block file is stored asa block file, etc.). In another example, the storage unit control module170 encodes the data object utilizing an error coding dispersal storagefunction to produce encoded data slices and stores the encoded dataslices in one or more of the memories 1-12. Note that the storage unitcontrol module unit may determine to utilize only the memories 1-12 ofthe DS unit 1 when the capabilities of memories 1-12 substantially meetthe requirements. In another example, the storage unit control module170 determines to utilize some combination of the memories 1-12 of theDS unit and memory of at least one other DS unit when the capabilitiesof memories 1-12 alone substantially do not meet the requirements.

In an example of operation, the storage unit control module 170determines where (e.g., which address of one or more of the memories) tostore the received data object as encoded data slices. Such adetermination may be based on one or more of metadata, a command (e.g.,from the DS processing unit indicating which memory or memory type touse), a type of data indicator, a local virtual DSN address to physicallocation table lookup, a priority indicator, a security indicator,available memory, memory performance data, memory status, memory costdata, and any other parameter to facilitate desired levels of efficiencyand performance. For instance, the storage unit control module 170 mayselect memories 1-12 (e.g., magnetic hard disk drives) to store theencoded data slices since the performance and efficiency is good enoughfor the requirements (e.g., availability, cost, response time). Inanother instance, the storage unit control module 170 distributes theslices to memories 1-10 when memories 11 and 12 are not available. Inanother instance, the storage unit control module 170 distributes theslices at various addresses across one memory. In another instance, thestorage unit control module 170 distributes a read threshold k=8 of theencoded data slices across memories 1-8 (for fast retrieval) and theother 4 (n-k) encoded data slices to other DS units. In yet anotherinstance, the storage unit control module 170 distributes the encodeddata slices across the DS unit memories and at least one other DS unitat the same site as the DS unit 1. In yet another instance, the storageunit control module 170 distributes the encoded data slices across theDS unit memories and at least one other DS unit at a different site asthe DS unit 1.

In a further example of operation, the storage unit control module 170creates and maintains a local virtual DSN address to physical memorytable. The storage unit control module 170 determines where previouslystored encoded data slices are located based on the local virtual DSNaddress to physical memory table upon receiving a retrieve request viathe network 24. Note that a DS processing unit operably coupled to theDS unit 1 via the network, maintains a virtual DSN address to physicalmemory table for the system tracking where the pillars are located foreach vault.

In the example of operation, the storage unit control module 170determines when a change has occurred to the memory configuration of theDS unit 1 and updates the local virtual DSN address to physical memorytable (e.g., DS unit level) and sends a configuration update message tothe DS processing unit to update the virtual DSN address to physicalmemory table (e.g., system level) based on the memory configurationchange. The storage unit control module 170 determines when a change hasoccurred to the memory configuration of the DS unit 1 based on one ormore of a configuration message from the DS managing unit, a memoryquery, a test, an error message, a configuration indicator, a command, avault lookup, a command, a predetermination, and a DS unit message. Forinstance, the storage unit control module 170 of DS unit 1 in FIG. 12Bdetermines that a change (e.g., memory 7-12 has been removed, which isutilized to store pillars 7-12 of vault 301) has occurred based on aquery of the memories 1-12.

In another instance, any number of pillars may be moved (e.g., viamemory transport) from one DS unit to another. In another instance, thestorage unit control module 170 of DS unit 2 in FIG. 12B determines thata change (e.g., memory 7-12 has been added which holds slices frompillars 7-12 of vault 301) has occurred based on a query of the memories1-12 and a DS managing unit configuration message. Next, storage unitcontrol module 170 of DS unit 1 in FIG. 12B updates its associated localDSN address to physical location table and send a configuration updatemessage to the DS processing unit where the message includes anindication that pillars 1-6 (e.g., of a vault 301) are stored in DS unit1 and/or pillars 7-12 are not stored in DS unit 1. The storage unitcontrol module 170 of DS unit 2 in FIG. 12B updates its associated localDSN address to physical location table and send a configuration updatemessage to the DS processing unit where the message includes anindication that pillars 7-12 (e.g., of vault 301) are stored in DS unit2. The DS processing unit utilizes the DS units to access the pillars ofthe new configuration. The DS units provide slice access for the pillarsof the new configuration.

FIG. 13 is another schematic block diagram of another embodiment of acomputing system. As illustrated, the system includes a processingmodule 50 (e.g., hosting the file application), a data object cache 172,a DS processing 34, and a dispersed storage network (DSN) memory 22. Inan implementation embodiment, the processing module 50, data objectcache 172, and DS processing 34 may be implemented as part of a userdevice 12. In another implementation embodiment, the processing module50 and data object cache 172 may be implemented as part of a user device12 and the DS processing 34 may be implemented as part of a DSprocessing unit 16.

The processing module 50 may be part of the computing core 26 of FIG. 2and may include memory to run a file application and store a workingcopy of a file. The processing module 50 may host a file application,which during a first timeframe manipulates a first portion of the file.In an example, the manipulation may include one or more of reading,editing, deleting, moving, inserting, replicating, and checking status.The file application may manipulate a second portion of the file duringa second timeframe etc.

The data object cache 172 may comprise memory to temporarily store atleast a portion of the file. The contents of the data object cache 172may change frequently as the file is manipulated. The file may bedeleted from the data object cache 172 once the manipulation sequencesconclude. Portions of the file may be stored as slices 11 in the DSNmemory 22 from time to time.

In an example of operation, DS processing 34 stores and/or retrievesslices 11 of the file in the DSN memory 22. For instance, the DSprocessing 34 determines to select at least a portion of the file,segment the portion, encode, and slice the portion to produce encodeddata slices in accordance with an error coding dispersal storagefunction. Next, the DS processing 34 send the encoded data slices to theDSN memory 22 for storage therein. In another instance, the DSprocessing 34 moves the portion of the file from the processing module50 to the data object cache 172. The determination to save the portionin DSN memory 22 may be based on one or more of an action policy (e.g.,when the file has changed), a query for change, a message from theprocessing module file application, and a timer expiration since thelast save sequence. The method to determine if the data object haschanged and what action to take when it has changed is described ingreater detail with reference to FIG. 14.

FIG. 14 is a flowchart illustrating an example of storing data. Themethod begins with step 174 where a processing module determines if adata object has changed based one or more of a query for change, amessage from the processing module file application, a changedetermination policy, a degree of change detection, a comparison of thefile to a copy of the file in the data object cache, and a timerexpiration since the last save sequence. For example, the processingmodule determines that the data object has not changed when a comparisonof the file to the file previously stored in the data object cache(e.g., as a result of the last save sequence) reveals that less than athreshold of characters are different.

In another example, the processing module determines that the dataobject has changed when a comparison of the file to the file previouslystored in the data object cache (e.g., as a result of the last savesequence) reveals that more than a threshold of characters are differentand the timer from the last save sequence has expired. In anotherexample, the processing module determines that the data object haschanged when the processing module receives a message that the file hasbeen closed (e.g., ending the file manipulation). The method repeatsback to step 174 when the processing module determines that the dataobject has not changed. The method continues to step 176 when theprocessing module determines that the data object has changed.

The method continues at step 176 where the processing module determinesoperational parameters including pillar width n, read threshold k, andan action policy (e.g., what to do when change is determined). Such adetermination may be based on one or more of a vault lookup, a command,a predetermination, and a message. The method continues at step 178where the processing module determines an action where the action mayinclude storing a new copy of the file in the data object cache (e.g.,in the file format and/or as encoded data slices) and/or storing a newcopy, revision, or portion of the file in a dispersed storage network(DSN) memory as encoded data slices. Such a determination may be basedon one or more of the action policy, the operational parameters, a datasize indicator, a system activity level indicator, a vault lookup, acommand, a message from the processing module, a predetermination, and amessage. For example, the processing module determines the action to bestore in the data object cache when the action policy indicates to storethe file in the cache when the data size is below a threshold.

In another example, the processing module determines the action to bestore in the DSN memory when the action policy indicates to store thefile in the DSN memory when the system level activity level indicator isbelow a threshold. The method branches to step 182 when the processingmodule determines the action to be store in the DSN memory. The methodcontinues to step 180 when the processing module determines the actionto be store in the data object cache. The method continues at step 180where the processing module saves the file in the data object cache inthe file format. For instance, the processing module saves the entirefile. In another instance, the processing module saves a portion of thefile that has changed since the last save sequence. Note that theprocessing module may create encoded data slices from the file inaccordance with the operational parameters and store the slices in thedata object cache. The method continues at step 22 where the processingmodule encodes a portion of the file in accordance with an error codingdispersal storage function to produce encoded data slices. Theprocessing module sends the encoded data slices to the DSN memory withan updated revision number and a store command for storage in the DSNmemory.

FIG. 15 is a flowchart illustrating an example of retrieving data. Themethod begins with step 184 where a processing module receives a dataobject retrieval request message from a requester (e.g., an applicationthat does not require the entire data object all at once includingexamples such as a media player, a text editor, etc.). Such a requestmay include one or more of a user ID, a data object name, a currentposition pointer (e.g., pointer within the data object), data objectsize, data type, a priority indicator, a security indicator, aperformance indicator, a command, and a message.

The method continues at step 186 where the processing module determinesoperational parameters which may include one or more of pillar width n,read threshold k, and a cache list (e.g., which data object may be wherein the data object cache). Such a determination may be based on one ormore of a vault lookup, a command, a predetermination, a data objectname, data object size, data type, a priority indicator, a securityindicator, a performance indicator, a command, and a message.

The method continues at step 188 where the processing module determinesa location of the data object which may include a data object cacheand/or a dispersed storage network (DSN) memory. Such a determinationmay be based on one or more of the operational parameters, a cache list,a vault lookup, a command, a predetermination, a data object name, dataobject size, data type, a priority indicator, a security indicator, aperformance indicator, a command, and a message. The method branches tostep 196 when the processing module determines the location of the dataobject to be not in the cache. The method continues to step 190 when theprocessing module determines the location of the data object to be inthe cache.

The method continues at step 190 where the processing module retrievesthe data object from the cache memory in accordance with a cache list.In an example, the data object is stored as encoded data slices. Theprocessing module de-slices and decodes the encoded data slices inaccordance with an error coding dispersal storage function to producethe data object in accordance with the operational parameters when thedata object is stored as encoded data slices. The method continues atstep 192 where the processing module sends the data object to therequester. The method branches to step 194.

The method continues at step 196 where the processing module retrievesencoded data slices from the DSN memory in accordance with theoperational parameters and/or location determination when the processingmodule determines the location of the data object to be not in thecache. The method continues at step 198 where the processing modulede-slices and decodes the slices utilizing the error coding dispersalstorage function and in accordance with the operational parameters toproduce the data object. The method continues at step 200 where theprocessing module stores the data object in data object cache memory andmodifies the cache list to indicate that the data object is stored inthe cache. Note that this may provide an improvement to the system suchthat the subsequent retrievals may be from the cache (e.g., faster). Themethod continues at step 202 where the processing module sends the dataobject to the requester. The method branches to step 194.

The method continues at step 194 where the processing module determinesa read ahead which may include an amount of the data object to retrievenext (e.g., which may be similar to the last retrieval if theconsumption pace is steady or it may be none). Such a determination maybe based on one or more of the amount of the data object retrieved forconsumption so far, the current position pointer, a history of readingahead, time since the last retrieval, the operational parameters, acache list, a vault lookup, a command, a predetermination, a data objectname, data object size, data type, a priority indicator, a securityindicator, a performance indicator, a command, a system activity levelindicator, and a message. For example, the processing module determinesthe read ahead to be 10 megabytes when the history of reading aheadindicates that the last five read ahead retrievals where 10 mega bytesand the average time between retrievals was 5 minutes. The methodrepeats back to step 184.

FIG. 16 is another flowchart illustrating another example of storingdata. The method begins with step 204 where a processing module (e.g.,of a dispersed storage (DS) processing unit) receives a store dataobject message. The store data object message may include one or more ofa command, a request, a user identity (ID), a data object name, arevision number, a data type, a data size, a priority indicator, asecurity indicator, a performance indicator, and metadata. The methodcontinues at step 206 where the processing module determines operationalparameters. Such operational parameters may include one or more ofpillar width n, read threshold k, a write threshold (e.g., minimumnumber of pillars to confirm a successful write to confirm the storesequence), a transaction number, and identifiers of DS unit to utilizefor storage. Such a determination may be based on one or more of a vaultlookup, a virtual DSN address to physical location table lookup, atransaction number list, a last transaction number, a predetermination,a revision number, a query of DSN, a command, a user ID, a data objectname, a data type, a data size, a priority indicator, a securityindicator, a performance indicator, and other metadata. For example, theprocessing module determines that a first transaction number is 731based on the last transaction number utilized was 730.

The method continues at step 208 where the processing module dispersedstorage error encodes the data in accordance with the operationalparameters to produce a set of encoded data slices. The method continuesat step 210 where the processing module generates a first transactionidentifier regarding storage of the set of encoded data slices. Notethat the first transaction identifier may include a transaction numberand/or a request number. Such a generation of the first transactionidentifier may include at least one of utilizing a coordinated universaltime, utilizing a random number generator output, performing a function(e.g., increment, decrement, multiply times 2, etc.) based on at leastone of a previous first transaction identifier and a previous secondtransaction identifier, performing a second function on the firsttransaction identifier to generate the second transaction identifier.

The processing module outputs a plurality of write request messages to aplurality of dispersed storage (DS) units, wherein each of the pluralityof write request messages includes the first transaction identifier anda corresponding one of the set of encoded data slices. One or more ofthe DS units may send a write response message (e.g., anacknowledgement) to the processing module in response to receiving thewrite request message. The processing module receives write responsemessages from the DS units. Note that the processing module may notreceive an acknowledgement due to many potential errors and failures(e.g., DS unit failure, network failure, etc.).

The method continues at step 212 where the processing module receiveswrite response messages from at least some of the DS units, wherein eachof the write response messages includes a reference to the firsttransaction identifier. Note that a write response message of the writeresponse messages comprises at least one of an operation succeededstatus code, a transaction conflict status code (e.g., slice is lockedby another transaction), an addressing error status code (e.g., slice isnot assigned to a responding DS unit), a check condition status code(e.g., an expected revision does not match what is currently stored),and an unauthorized status code (e.g., a requester is not authorized towrite the slice).

The processing module determines whether a write threshold number offavorable (e.g., with the operation succeeded status code) writeresponse messages have been received within a time period. The methodbranches to step 216 when the processing module determines that thewrite threshold number of favorable write response messages have beenreceived within the time period. The method continues to step 214 whenthe processing module determines that the write threshold number offavorable write response messages have not been received within the timeperiod. Alternatively, the processing module determines that the writethreshold number of favorable write response messages have not beenreceived within the time period when the processing module receives atleast one of the write response messages having an unfavorable responseand, when a number of write response messages having the unfavorableresponse exceeds a second threshold. The method continues at step 214where the processing module outputs a plurality of rollback transactionrequest messages to the plurality of DS units, wherein each of theplurality of rollback transaction request messages includes the firsttransaction identifier. Note that the DS unit deletes the encoded dataslice, slice names, and first transaction identifier in response toreceiving the rollback transaction request message. Next, the methodbranches back to step 208 where the processing module re-attempts tostore the set of encoded data slices.

The method continues at step 216 where the processing module readsdirectory information associated with the data. Such directoryinformation may link a data identifier and revision identifier to avirtual DSN address of the location where the encoded data slices arestored in the DS units of the dispersed storage network memory. In anexample, the processing module retrieves encoded directory slices fromthe plurality of DS units and decodes the encoded directory slicesutilizing an error coding dispersal stored function to produce thedirectory information. The processing module updates directoryinformation regarding storage of the data to produce updated directoryinformation. For example, the processing module modifies the revisionidentifier to indicate a newer revision has been stored for thecorresponding data identifier.

The method continues at step 218 where the processing module determinesif the directory information is as expected by one of more of comparinga transaction number of the last directory addition to an expected nexttransaction number (e.g., from the transaction number list) and bycomparing the last entered data object name to the current data objectname. Note that it is possible that another processing module isconcurrently writing slices of a data object where the data object istargeted for the same directory position (e.g., a write collision). Themethod branches to step 222 when the processing module determines thatthe directory information is as expected. The method continues to step220 when the processing module determines that the directory informationis not as expected. The method continues at step 220 where theprocessing module sends an error message (e.g., to a dispersed storagemanaging unit), and may send a rollback request message to the pluralityof DS units, and may branch back to step 208 to re-create and re-storeencoded data slices to avoid a potential write conflict.

The method continues at step 222 where the processing module dispersedstorage error encodes the updated directory information to produce a setof encoded directory slices next. Next, the processing module generatesa second transaction identifier regarding storage of the set of encodeddirectory slices wherein generating the second transaction identifierincludes at least one of utilizing a coordinated universal time,utilizing a random number generator output, performing a function basedon at least one of a previous transaction identifier, a previous secondtransaction identifier, performing a second function on the firsttransaction identifier to generate the second transaction identifier.The processing module outputs a second plurality of write requestmessages to a second plurality of DS units, wherein each of the secondplurality of write request messages includes the second transactionidentifier and a corresponding one of the set of encoded directoryslices. Alternatively, the processing module outputs the secondplurality of write request messages to the plurality of DS units.

Alternatively, the processing module outputs a plurality of read requestmessages that includes a plurality of slice names corresponding to theupdated directory information. Next, the processing module receives aplurality of read response messages that include a slice revision. Next,the processing module establishes the expected slice revision as theslice revision. Next, the processing module outputs the second pluralityof write request messages to the plurality of DS units, wherein each ofthe second plurality of write request messages further includes theexpected slice revision. The DS units may send an acknowledgement to theDS processing in response to receiving the data object name and secondtransaction number.

The processing module receives second write response messages (e.g.,acknowledgements) from at least some of the plurality of DS units.Alternatively, the processing module interprets the second writeresponse messages for confirmation of the expected slice revision. Notethat the second write response message of the second write responsemessages comprises at least one of an operation succeeded status code, atransaction conflict status code, an addressing error status code, acheck condition status code (e.g., the expected slice revision does notequal a current slice revision), and an unauthorized status code. Notethat the processing module may not receive a second write responsemessage due to many potential errors and failures (e.g., DS unitfailure, network failure).

The method continues at step 224 where the processing module determineswhether at least a second write threshold number of favorable (e.g.,operation succeeded without error) second write response messages havebeen received from the DS units within a time period. The methodbranches back to step 216 where the processing module re-updates (e.g.,re-reads and updates) the directory information regarding storage of thedata, re-disperse error encodes the directory information to re-producethe set of encoded directory slices, and outputs at least some of thesecond plurality of write request messages regarding the reproduced setof encoded directory slices at step 222 to try again when the processingmodule determines that at least the second write threshold number offavorable second write response messages have not been received within atime period. The method continues to step 226 when the processing moduledetermines that at least the second write threshold number of favorablesecond write response messages have been received.

The method continues at step 226 where the processing module outputs aplurality of data commit request messages regarding the set of encodeddata slices to the plurality of DS units, wherein each of the pluralityof data commit request messages includes the first transactionidentifier. Next, the processing module outputs the plurality ofdirectory commit request messages regarding the set of encoded directoryslices to the second plurality of DS units, wherein each of theplurality of directory commit request messages includes the secondtransaction identifier. Alternatively, the processing module outputs aplurality of commit request messages regarding the set of encoded dataslices and the set of encoded directory slices to the plurality of DSunits, wherein each of the plurality of commit request messages includesthe first and second transaction identifiers. Alternatively, theprocessing module outputs the plurality of commit request messagesregarding the set of encoded data slices and the set of encodeddirectory slices to the plurality of DS units. The method of operationof the DS unit is discussed in greater detail with reference to FIG. 17.

FIG. 17 is a flowchart illustrating an example of storing an encodeddata slice. The method begins with step 228 where a processing module(e.g., of a dispersed storage (DS) unit) receives a write requestmessage from a dispersed storage (DS) processing module, wherein thewrite request message includes a slice name (e.g., of the slice tostore), a DS processing module most-recent slice revision, a new slicerevision (e.g., of the slice to store), and an encoded directory sliceof directory information regarding storage of data. Note that DSprocessing module most-recent slice revision may be a revision numberthat the processing module of the DS unit previously sent to the DSprocessing module in response to a previous encoded directory slicequery.

The method continues at step 230 where the processing module obtains aDS unit most-recent slice revision from local memory based on the slicename. The method continues at step 232 where the processing moduledetermines whether the DS unit most-recent slice revision comparesfavorably to the DS processing module most-recent slice revision fromthe request. The processing module determines that the DS unitmost-recent slice revision compares favorably to the DS processingmodule most-recent slice revision when the DS unit most-recent slicerevision is substantially the same as the DS processing modulemost-recent slice revision. In addition, the processing module may checkfor other possible error conditions. In an example, the processingmodule verifies that the slice name is within a range that is assignedto the processing module (e.g., the DS unit). The processing modulesends a write response message that includes an addressing error statuscode when the processing module determines that the slice name is notwithin the range. In another example, the processing module verifiesthat a requester that initiated the write request is authenticated andhas an appropriate permissions level. The processing module sends awrite response message that includes an unauthorized status code whenthe processing module determines that requester is not authenticated ordoes not have the appropriate permissions level.

The method branches to step 236 when the processing module determinesthat the DS unit most-recent slice revision compares favorably to the DSprocessing module most-recent slice revision. The method continues tostep 234 when the processing module determines that the DS unitmost-recent slice revision compares unfavorably to the DS processingmodule most-recent slice revision. The method continues at step 234where the processing module generates a write response message toinclude a condition status code (e.g., a check condition status code)indicating the unfavorable comparison. Next, the processing module sendsthe write response message to the DS processing module.

The method continues at step 236 where the processing module stores theencoded directory slice. In addition, the processing module may generatea write response message that includes an operation succeeded statuscode. Next, the processing module sends the write response message tothe DS processing module. The method continues at step 238 where theprocessing module stores the new slice revision as the DS unitmost-recent slice revision when the transaction identifier is null. Theprocessing module stores the new slice revision as the DS unit mostrecent slice revision when the transaction identifier is not null and acommit transaction message is subsequently received as discussed below.

Alternatively, or in addition to, the processing module receives thewrite request message, wherein the write request message furtherincludes a DS processing module transaction identifier. Next, theprocessing module determines whether the slice name has a locked statebased on a local state indicator. The processing module generates awrite response message that includes a transaction conflict status codeand sends the write response message to the DS processing module whenthe slice name has the locked state and a DS unit transaction indicatorassociated with the encoded directory slice compares unfavorably to theDS processing module transaction identifier. The processing moduleupdates the local state indicator to indicate that the slice name hasthe locked state and stores the DS processing module transactionidentifier as the DS unit transaction identifier when the slice namedoes not have a locked state.

In addition, the processing module may receive a commit transactionrequest message regarding storage of at least one of an encoded dataslice and an encoded directory slice, wherein the commit transactionrequest message includes at least one transaction identifier. Next, theprocessing module identifies one or more slice names based on the atleast one transaction identifier and for each of the one or more slicesnames, updates a slice status indicator to indicate the at least one ofthe encoded data slice and the encoded directory slice is visible. Inaddition, the processing module may update a current revision indicatorassociated with the slice name and transaction identifier to indicate arevision associated with the slice name. In addition, the processingmodule may update the slice status indicator to indicate that the slicename has an unlocked state subsequent to indicating that the at leastone of the encoded data slice and the encoded directory slice isvisible.

Alternatively, the processing module receives a commit transactionrequest message regarding storage of at least one of an encoded dataslice and an encoded directory slice, wherein the commit transactionrequest message includes first and second transaction identifiers of theat least one transaction identifier, wherein the first transactionidentifier is associated with the encoded data slice and the secondtransaction identifier is associated with the encoded directory slice.Next, the processing module updates a first slice status indicator toindicate that the encoded data slice is visible, and re-updates thefirst slice status indicator to indicate that the encoded data slice isnot visible when a DS unit memory error exists. The processing moduleupdates a second slice status indicator to indicate that the encodeddirectory slice is visible and re-updates the second slice statusindicator to indicate that the encoded directory slice is not visiblewhen the DS unit memory error exists.

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “operably coupled to”, “coupled to”, and/or “coupling” includesdirect coupling between items and/or indirect coupling between items viaan intervening item (e.g., an item includes, but is not limited to, acomponent, an element, a circuit, and/or a module) where, for indirectcoupling, the intervening item does not modify the information of asignal but may adjust its current level, voltage level, and/or powerlevel. As may further be used herein, inferred coupling (i.e., where oneelement is coupled to another element by inference) includes direct andindirect coupling between two items in the same manner as “coupled to”.As may even further be used herein, the term “operable to” or “operablycoupled to” indicates that an item includes one or more of powerconnections, input(s), output(s), etc., to perform, when activated, oneor more its corresponding functions and may further include inferredcoupling to one or more other items. As may still further be usedherein, the term “associated with”, includes direct and/or indirectcoupling of separate items and/or one item being embedded within anotheritem. As may be used herein, the term “compares favorably”, indicatesthat a comparison between two or more items, signals, etc., provides adesired relationship. For example, when the desired relationship is thatsignal 1 has a greater magnitude than signal 2, a favorable comparisonmay be achieved when the magnitude of signal 1 is greater than that ofsignal 2 or when the magnitude of signal 2 is less than that of signal1.

While the transistors in the above described figure(s) is/are shown asfield effect transistors (FETs), as one of ordinary skill in the artwill appreciate, the transistors may be implemented using any type oftransistor structure including, but not limited to, bipolar, metal oxidesemiconductor field effect transistors (MOSFET), N-well transistors,P-well transistors, enhancement mode, depletion mode, and zero voltagethreshold (VT) transistors.

The present invention has also been described above with the aid ofmethod steps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claimed invention.

The present invention has been described, at least in part, in terms ofone or more embodiments. An embodiment of the present invention is usedherein to illustrate the present invention, an aspect thereof, a featurethereof, a concept thereof, and/or an example thereof. A physicalembodiment of an apparatus, an article of manufacture, a machine, and/orof a process that embodies the present invention may include one or moreof the aspects, features, concepts, examples, etc., described withreference to one or more of the embodiments discussed herein.

The present invention has been described above with the aid offunctional building blocks illustrating the performance of certainsignificant functions. The boundaries of these functional buildingblocks have been arbitrarily defined for convenience of description.Alternate boundaries could be defined as long as the certain significantfunctions are appropriately performed. Similarly, flow diagram blocksmay also have been arbitrarily defined herein to illustrate certainsignificant functionality. To the extent used, the flow diagram blockboundaries and sequence could have been defined otherwise and stillperform the certain significant functionality. Such alternatedefinitions of both functional building blocks and flow diagram blocksand sequences are thus within the scope and spirit of the claimedinvention. One of average skill in the art will also recognize that thefunctional building blocks, and other illustrative blocks, modules andcomponents herein, can be implemented as illustrated or by discretecomponents, application specific integrated circuits, processorsexecuting appropriate software and the like or any combination thereof.

What is claimed is:
 1. A method for execution by a computing device, themethod comprises: independently executing a first write transaction in adispersed storage network (DSN) to a particular write verification stepof a multiple step write process, wherein the first write transactionhas a first transaction identifier; independently executing a secondwrite transaction in the DSN to the particular write verification step,wherein the second write transaction has a second transactionidentifier, and wherein subject matter of the first write transaction isrelated to subject matter of the second write transaction; and when eachof the first and second write transactions have reached the particularwrite verification step, dependently finalizing the multiple step writeprocess for each of the first and second write transactions utilizingthe first and second transaction identifiers.
 2. The method of claim 1further comprises: the first write transaction includes a first set ofwrite commands for a data segment that has been dispersed storage errorencoded into a set of encoded data slices; and the second writetransaction includes a second set of write commands for directoryinformation regarding the set of encoded data slices, wherein thedirectory information is dispersed storage error encoded into a set ofencoded directory slices.
 3. The method of claim 1, wherein the multiplestep write process further comprises: a write initiate step thatincludes a set of write requests and a write threshold number ofcorresponding write responses; a write commit step that includes a setof write commit requests and the write threshold number of correspondingwrite commit responses; and a write finalize step that includes a set ofwrite finalize commands, wherein the particular step is the writeinitiate step.
 4. The method of claim 1, wherein the multiple step writeprocess further comprises: a write initiate step that includes a set ofwrite requests and a write threshold number of corresponding writeresponses; a write commit step that includes a set of write commitrequests and the write threshold number of corresponding write commitresponses; and a write finalize step that includes a set of writefinalize commands, wherein the particular step is the write commit step.5. The method of claim 1, wherein the independently executing the firstwrite transaction further comprises: generating the first transactionidentifier regarding storage of a set of encoded data slices, wherein adata segment was dispersed storage error encoded to produce the set ofencoded data slices; outputting a set of write request messages todispersed storage (DS) units of the DSN, wherein each write requestmessage of the set of write request messages includes the firsttransaction identifier and a corresponding one of the set of encodeddata slices; receiving write response messages from at least some of theDS units, wherein each of the write response messages includes areference to the first transaction identifier; and when at least a writethreshold number of the write response messages have been received,commencing a commit step of the multiple step write process for thefirst write transaction.
 6. The method of claim 5, wherein thecommencing the commit step for the first write transaction comprises:outputting a plurality of data commit request messages regarding the setof encoded data slices to the DS units, wherein each of the plurality ofdata commit request messages includes the first transaction identifier.7. The method of claim 1, wherein the independently executing the secondwrite transaction further comprises: generating the second transactionidentifier regarding storage of a set of encoded directory slices,wherein directory information is dispersed storage error encoded toproduce a set of encoded directory slices; outputting a second pluralityof write request messages to DS units, wherein each of the secondplurality of write request messages includes the second transactionidentifier and a corresponding one of the set of encoded directoryslices; and when at least a second write threshold number of favorablesecond write response messages have been received from the DS units,commencing a commit step of the multiple step write process for thesecond write transaction.
 8. The method of claim 7, wherein thecommencing the commit step for the second write transaction comprises:outputting a plurality of directory commit request messages regardingthe set of encoded directory slices to the DS units, wherein each of theplurality of directory commit request messages includes the secondtransaction identifier.
 9. A computer comprises: an interface; memory;and a processing module operably coupled to the memory and theinterface, wherein the processing module is operable to: independentlyexecute a first write transaction in a dispersed storage network (DSN)to a particular write verification step of a multiple step writeprocess, wherein the first write transaction has a first transactionidentifier; independently execute a second write transaction in the DSNto the particular write verification step, wherein the second writetransaction has a second transaction identifier, and wherein subjectmatter of the first write transaction is related to subject matter ofthe second write transaction; and when each of the first and secondwrite transactions have reached the particular write verification step,dependently finalize the multiple step write process for each of thefirst and second write transactions utilizing the first and secondtransaction identifiers.
 10. The computer of claim 9 further comprises:the first write transaction including a first set of write commands fora data segment that has been dispersed storage error encoded into a setof encoded data slices; and the second write transaction including asecond set of write commands for directory information regarding the setof encoded data slices, wherein the directory information is dispersedstorage error encoded into a set of encoded directory slices.
 11. Thecomputer of claim 9, wherein the processing module is further operableto: output, via the interface, a write initiate step that includes a setof write requests and a write threshold number of corresponding writeresponses; output, via the interface, a write commit step that includesa set of write commit requests and the write threshold number ofcorresponding write commit responses; and output, via the interface, awrite finalize step that includes a set of write finalize commands,wherein the particular step is the write initiate step.
 12. The computerof claim 9, wherein the processing module is further operable to:output, via the interface, a write initiate step that includes a set ofwrite requests and a write threshold number of corresponding writeresponses; output, via the interface, a write commit step that includesa set of write commit requests and the write threshold number ofcorresponding write commit responses; and output, via the interface, awrite finalize step that includes a set of write finalize commands,wherein the particular step is the write commit step.
 13. The computerof claim 9, wherein the processing module is further operable to:generate the first transaction identifier regarding storage of a set ofencoded data slices, wherein a data segment was dispersed storage errorencoded to produce the set of encoded data slices; output, via theinterface, a set of write request messages to dispersed storage (DS)units of the DSN, wherein each write request message of the set of writerequest messages includes the first transaction identifier and acorresponding one of the set of encoded data slices; receive, via theinterface, write response messages from at least some of the DS units,wherein each of the write response messages includes a reference to thefirst transaction identifier; and when at least a write threshold numberof the write response messages have been received, commence a commitstep of the multiple step write process for the first write transaction.14. The computer of claim 13, wherein the processing module furtherfunctions to commence the commit step for the first write transactionby: outputting, via the interface, a plurality of data commit requestmessages regarding the set of encoded data slices to the DS units,wherein each of the plurality of data commit request messages includesthe first transaction identifier.
 15. The computer of claim 9, whereinthe processing module further functions to independently execute thesecond write transaction by: generating the second transactionidentifier regarding storage of a set of encoded directory slices,wherein directory information is dispersed storage error encoded toproduce a set of encoded directory slices; outputting, via theinterface, a second plurality of write request messages to DS units,wherein each of the second plurality of write request messages includesthe second transaction identifier and a corresponding one of the set ofencoded directory slices; and when at least a second write thresholdnumber of favorable second write response messages have been receivedfrom the DS units, commencing a commit step of the multiple step writeprocess for the second write transaction.
 16. The computer of claim 15,wherein the processing module further functions to commence the commitstep for the second write transaction by: outputting, via the interface,a plurality of directory commit request messages regarding the set ofencoded directory slices to the DS units, wherein each of the pluralityof directory commit request messages includes the second transactionidentifier.